(Delphi ActiveX) RSA-OAEP with SHA256 hashing

RSA encrypt a SHA256 hash with OAEP padding.

Chilkat for Delphi Downloads Chilkat ActiveX DLL for Delphi Chilkat non-ActiveX DLL for Delphi * The examples here use the ActiveX DLL.

uses
    Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
    Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls, Chilkat_TLB;

...

procedure TForm1.Button1Click(Sender: TObject);
var
pubkey: TPublicKey;
sbPem: TChilkatStringBuilder;
bCrlf: Integer;
success: Integer;
json: TChilkatJsonObject;
rsa: TChilkatRsa;
bUsePrivateKey: Integer;
encryptedStr: WideString;

begin
// This example requires the Chilkat API to have been previously unlocked.
// See Global Unlock Sample for sample code.

pubkey := TPublicKey.Create(Self);

sbPem := TChilkatStringBuilder.Create(Self);
bCrlf := 1;
sbPem.AppendLine('-----BEGIN PUBLIC KEY-----',bCrlf);
sbPem.AppendLine('MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEA33TqqLR3eeUmDtHS89qF',bCrlf);
sbPem.AppendLine('3p4MP7Wfqt2Zjj3lZjLjjCGDvwr9cJNlNDiuKboODgUiT4ZdPWbOiMAfDcDzlOxA',bCrlf);
sbPem.AppendLine('04DDnEFGAf+kDQiNSe2ZtqC7bnIc8+KSG/qOGQIVaay4Ucr6ovDkykO5Hxn7OU7s',bCrlf);
sbPem.AppendLine('Jp9TP9H0JH8zMQA6YzijYH9LsupTerrY3U6zyihVEDXXOv08vBHk50BMFJbE9iwF',bCrlf);
sbPem.AppendLine('wnxCsU5+UZUZYw87Uu0n4LPFS9BT8tUIvAfnRXIEWCha3KbFWmdZQZlyrFw0buUE',bCrlf);
sbPem.AppendLine('f0YN3/Q0auBkdbDR/ES2PbgKTJdkjc/rEeM0TxvOUf7HuUNOhrtAVEN1D5uuxE1W',bCrlf);
sbPem.AppendLine('SwIDAQAB',bCrlf);
sbPem.AppendLine('-----END PUBLIC KEY-----',bCrlf);

// Load the public key object from the PEM. 
success := pubkey.LoadFromString(sbPem.GetAsString());
if (success <> 1) then
  begin
    Memo1.Lines.Add(pubkey.LastErrorText);
    Exit;
  end;

// Build a small string to encrypt
json := TChilkatJsonObject.Create(Self);
json.UpdateString('example','123');
json.UpdateString('hello','world');
Memo1.Lines.Add(json.Emit());

// This is the JSON to be RSA encrypted:  {"example":"123","hello":"world"}

// IMPORTANT: RSA encryption is only used to encrypt small amounts of data.
// RSA is only able to encrypt data to a maximum amount of your key size (2048 bits = 256 bytes) 
// minus padding / header data (11 bytes for PKCS#1 v1.5 padding, 42 bytes for OAEP).
// As a result it is often not possible to encrypt files with RSA directly. 
// RSA is also not meant for this purpose. 
// 
// If you want to encrypt more data, you can use something like:
// 1) Generate a 256-bit random keystring K
// 2) Encrypt your data with AES-CBC with K
// 3) Encrypt K with RSA
// 4) Send both to the other side 

rsa := TChilkatRsa.Create(Self);
rsa.OaepPadding := 1;
rsa.OaepHash := 'SHA-256';
rsa.ImportPublicKeyObj(pubkey.ControlInterface);
rsa.EncodingMode := 'base64';

// Note: The OAEP padding uses random bytes in the padding, and therefore each time encryption happens,
// even using the same data and key, the result will be different --  but still valid.  One should not expect
// to get the same output.
bUsePrivateKey := 0;
encryptedStr := rsa.EncryptStringENC(json.Emit(),bUsePrivateKey);
if (rsa.LastMethodSuccess <> 1) then
  begin
    Memo1.Lines.Add(rsa.LastErrorText);
    Exit;
  end;

Memo1.Lines.Add('Result: ' + encryptedStr);
end;